Hi,
What is saved in the addres_country column of the hikashop_address table is indeed something like that, which is the namekey of the zone. If you look in the hikashop_zone table, you can see the namekey there.
Then, the namekey is automatically converted to the name of the country when the system is displaying the address.
Changing that to save something else than the zone_namekey would be quite complex as the system hasn't been made to use something else (like the zone ID or the zone name).
Even payment plugins or shipping plugins expect the address_country to contain a zone namekey. If you change that to something else, then payment/shipping plugins might not work properly.
So I would recommend against it.